Dynamical mean-field approach to materials with strong electronic correlations

We review recent results on the properties of materials with correlated electrons obtained within the LDA+DMFT approach, a combination of a conventional band structure approach based on the local density approximation (LDA) and the dynamical mean-field theory (DMFT). The application to four outstanding problems in this field is discussed: (i) we compute the full valence band structure of the charge-transfer insulator NiO by explicitly including the p-d hybridization, (ii) we explain the origin for the simultaneously occuring metal-insulator transition and collapse of the magnetic moment in MnO and Fe2O3, (iii) we describe a novel GGA+DMFT scheme in terms of plane-wave pseudopotentials which allows us to compute the orbital order and cooperative Jahn-Teller distortion in KCuF3 and LaMnO3, and (iv) we provide a general explanation for the appearance of kinks in the effective dispersion of correlated electrons in systems with a pronounced three-peak spectral function without having to resort to the coupling of electrons to bosonic excitations. These results provide a considerable progress in the fully microscopic investigations of correlated electron materials.Comment: 24 pages, 14 figures, final version, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom

Stochastic online scheduling on parallel machines

We consider a non-preemptive, stochastic parallel machine scheduling model with the goal to minimize the weighted completion times of jobs. In contrast to the classical stochastic model where jobs with their processing time distributions are known beforehand, we assume that jobs appear one by one, and every job must be assigned to a machine online. We propose a simple online scheduling policy for that model, and prove a performance guarantee that matches the currently best known performance guarantee for stochastic parallel machine scheduling. For the more general model with job release dates we derive an analogous result, and for NBUE distributed processing times we even improve upon the previously best known performance guarantee for stochastic parallel machine scheduling. Moreover, we derive some lower bounds on approximation

Scaling of metabolic rate with body mass and temperature in teleost fish

1. We examined published studies relating resting oxygen consumption to body mass and temperature in post-larval teleost fish. The resulting database comprised 138 studies of 69 species (representing 28 families and 12 orders) living over a temperature range of c. 40 °C. 2. Resting metabolic rate (Rb; mmol oxygen gas h–1) was related to body mass (M; wet mass, g) by Rb = aMb, where a is a constant and b the scaling exponent. The model was fitted by least squares linear regression after logarithmic transformation of both variables. The mean value of scaling exponent, b, for the 69 individual species was 0·79 (SE 0·11). The general equation for all teleost fish was 1nRb = 0·80(1nM) – 5·43. 3. The relationship between resting oxygen consumption and environmental temperature for a 50-g fish was curvilinear. A typical tropical fish at 30°C requires approximately six times as much oxygen for resting metabolism as does a polar fish at 0°C. This relationship could be fitted by several statistical models, of which the Arrhenius model is probably the most appropriate. The Arrhenius model for the resting metabolism of 69 species of teleost fish, corrected to a standard body mass of 50 g, was 1nRb = 15·7 – 5·02.T–1, where T is absolute temperature (103 × K). 4. The Arrhenius model fitted to all 69 species exhibited a lower thermal sensitivity of resting metabolism (mean Q10 = 1·83 over the range 0–30 °C) than typical within-species acclimation studies (median Q10 = 2·40, n = 14). This suggests that evolutionary adaptation has reduced the overall thermal sensitivity of resting metabolism across species. Analysis of covariance indicated that the relationships between resting metabolic rate and temperature for various taxa (orders) showed similar slopes but significantly different mean rates. 5. Analysis of the data for perciform fish provided no support for metabolic cold adaptation (the hypothesis that polar fish show a resting metabolic rate higher than predicted from the overall rate/temperature relationship established for temperate and tropical species). 6. Taxonomic variation in mean resting metabolic rate showed no relationship to phylogeny, although the robustness of this conclusion is constrained by our limited knowledge of fish evolutionary history